The transmission line models for printed circuit boards and packages are based on 85 ±15% differential impedance, and include both microstrip and stripline structures. The models for the cables are 90 ±7%. Impedance variation is incorporated into the full channel models. Note that the host PCB includes both stripline and microstrip routing, based on a 6-layer board stack-up. The via models cover a transition between the top layer to the 3rd layer from the top of the board. The device PCB uses only microstrips, as it is expected that minimum layer count boards are used. Package models include connections from the silicon to the package substrate, layer-to-layer connections within the substrate, and solder ball connections to the underlying PCB. Full link frequency responses are plotted in Figure 5 for both the short channel (device driving) and long channel (host driving) models. The plots indicate an insertion loss difference of more than 13dB at the fundamental frequency. In addition, the short channel shows approximately 6dB more NEXT than does the long channel. Chapter four will present time domain results (pulse responses) based upon these frequency responses.